This invention relates to capacitors and capacitor forming methods. This invention also related to field effect transistors, and to methods of forming field effect transistors.
As DRAMs increase in memory cell density, there is a continuing challenge to maintain sufficiently high storage capacitance despite decreasing cell area. Additionally, there is a continuing goal to further decrease cell area. One principal way of increasing cell capacitance is through cell structure techniques. Such techniques include three-dimensional cell capacitors, such as trenched or stacked capacitors. Yet as feature size continues to become smaller and smaller, development of improved materials for cell dielectrics as well as the cell structure are important. The feature size of 256 Mb DRAMs will be on the order of 0.25 micron or less, and conventional dielectrics such as SiO2 and Si3N4 might not be suitable because of small dielectric constants.
Insulating inorganic metal oxide materials, such as ferroelectric materials or perovskite materials or pentoxides such as tantalum pentoxide, have high dielectric constants and low leakage current which make them attractive as cell dielectric materials for high density DRAMs and non-volatile memories. Despite the advantages of high dielectric constants and low leakage, insulating inorganic metal oxide materials suffer from many drawbacks. For example, all of these materials incorporate oxygen or are otherwise exposed to oxygen for densification to produce the desired capacitor dielectric layer. Unfortunately, the provision of such layers or subjecting such layers to oxidation densification can undesirably oxidize the underlying bottom or lower storage node electrode where such is made of a readily oxidizable material. For example, Ta2O5 is typically subjected to an anneal in the presence of an oxygen ambient. The anneal drives any carbon present out of the layer and advantageously injects additional oxygen into the layer such that the layer uniformly approaches a stoichiometry of five oxygen atoms for every two tantalum atoms. The oxygen anneal is commonly conducted at a temperature of from about 400xc2x0 C. to about 1000xc2x0 C. utilizing one or more of O3, N2O and O2. The oxygen containing gas is typically flowed through a reactor at a rate of from about 0.5 slm to about 10 slm.
Dielectric materials are also used for gate dielectric regions in field effect transistors between a conductive gate and a semiconductive channel region. This invention is directed to improved methods and constructions associated with transistors and capacitors, particularly where higher dielectric constants are desired.
The invention comprises capacitors, capacitor forming methods, field effect transistors, and field effect transistor forming methods. In one aspect, a method of forming a layer including tungsten oxide includes forming a first layer including tungsten nitride over a substrate. In one implementation, the tungsten nitride layer is oxidized under conditions effective to form a second layer which comprises tungsten oxide. In one implementation, the tungsten nitride is oxidized under conditions effective to form a second layer at least a majority of which is tungsten trioxide. In one aspect, a capacitor forming method includes forming a first capacitor electrode layer over a substrate. A second layer including tungsten nitride is formed over the first capacitor electrode layer. A third capacitor electrode layer is formed over the second layer. The second layer is oxidized under conditions effective to transform at least some of the tungsten nitride into a tungsten trioxide comprising capacitor dielectric layer. Other capacitor forming methods are contemplated. The invention also includes capacitors formed by these and other methods.
In one aspect, a method of forming a field effect transistor includes forming a tungsten nitride comprising layer proximate at least one of a semiconductive channel region or a conductive gate layer. The tungsten nitride comprising layer is oxidized under conditions effective to transform at least some of the tungsten nitride to a tungsten oxide comprising gate dielectric layer. A transistor gate is provided operably proximate the gate dielectric layer, and source/drain regions are provided operably proximate the transistor gate. The invention also includes field effect transistors formed by this and other methods.